Already it is possible that mobile telephony networks and IMS networks are combined for various applications. E.g. a GSM subscriber attached to a mobile telephony network may obtain basic services, supplementary services and value added services associated with an IMS network. Hereto, the GSM subscriber is registered in the IMS network by means of a contact address associated with a public identifier used for that subscriber in the GSM network. However, up to now, this is restricted to voice call related applications in the IMS network. To enable for a GSM subscriber to use her GSM terminal for the sending and receiving of Short message services, but yet to receive basic services, supplementary services and value added services associated with an IMS network, separate, special messaging application servers are required in the IMS network.